Will Pine Trees Kill Nearby Plants?

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As pine trees mature, they shed needles that lie like an acidic carpet around their trunks. A myth exists that this gradually causes the soil to become acidic, killing nearby plants. In fact, however, pine tree needles barely affect the soil pH even when worked into the soil for that purpose. The real problem lies in whether other plants can survive having a mulch of pine tree needles around them. Choosing plants that tolerate pine trees, such as the Monterey pine (Pinus radiata) hardy to U.S. Department of Agriculture hardiness zones 7B through 9 and the shore pine (Pinus contorta) that thrives in USDA zones 7 and 8, can help your garden stay healthy.

Soil Acidity

Pine needles have a pH between 3.2 and 3.8, which means that they can turn the soil slightly more acidic if you work them into the soil as compost. However, if they merely fall from a tree and rest on top of the soil, they have almost no effect on the plant roots growing below the soil's surface. This is because microbes in the dirt neutralize the acidity as the needles decompose.

Pine Needle Mulch

As pines drop needles, they leave a mulch on the ground. Because of their dryness and waxy coating, pine needles are slow to decompose, which makes them inefficient as mulch; typically, a compost pile should include no more than 10 percent pine needles. On the other hand, pine needles mixed with other compost can help improve air flow in the pile.

Acidic Plants

Like many other evergreens, pine trees thrive in slightly acidic soil -- and that means other plants in the area should also appreciate the acidic soil they must share with the pines. Plants that do well in this soil pH level include some types of magnolias (Magnolia), such as southern magnolias that thrive in USDA zones 7 through 10A; hollies (Ilex), hardy up to USDA zone 9; and bigleaf hydrangeas (Hydrangea macrophylla), hardy in USDA zones 5B through 9A.

Shading

Though many types of plants can grow near pine trees, not as many can survive directly under pine trees or in their shadows. If you want to grow plants very close to pine trees, you'll need to find plants that tolerate shade much of the time. Examples include hollies (Ilex) and boxwoods (Buxus), such as common boxwood (Buxus sempervirens), which is hardy to USDA zones 6 through 8.